Treatment of olefin-containing aromatic hydrocarbons with acid and alkali



Aug. 7, 1951 2,563,628

S. VILES TREATMENT OF OLEFIN CONTAINING AROMATIC HYDROCARBONS WITH ACID AND ALKALI Filed April 29, 1950 ACID TREATED MID GAU8TI6 WASHED H FEED REHEATER urn NYDROGAIIOIIS 25 courncrnva sonwu KsuLromln-s QETTLING SECTION OM18 TIC .454 nursn FRESH OAUSTIG USED GAUQTIO srnu con.

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Patented Aug. 7, 1951 TREATMENT OF OLEFlN-CONTAININ G ARO- MATIC HYDROCARBONS WITH ACID AND ALKALI Prentiss S. Viles, Baytown, Tex., assignor, by

mesne assignments, to Standard Oil Development Company, Elizabeth, N. J., a corporation of Delaware Application April 29, 1950, Serial No. 158,997

'1 Claims. (Cl. 202-57) The present invention is directed to a method for treating aromatic hydrocarbon fractions and, particularly, is directed to treatment of aromatic hydrocarbon fractions comprising an appreciable amount of olefinic compounds.

Usually the aromatic hydrocarbon fractions will contain 1% and more of olefinic hydrocarbons. The present invention is specifically directed to an improvement in the process described and claimed in U. S. 2,400,373, issued May 14, 1946, in the name of Henry G. Schutze. The invention is also an improvement over U. S. 2,481,816, issued September 13, 1949, to John G. Browder et al.

The present invention contemplates improvements in the method of hydrolysis described and claimed in the aforementioned Schutze and Browder et al. patents and involves the steps of heating acid treated and caustic neutralized aromatic hydrocarbons to a temperature in the range between 300 and 350 E, the heated hydrocarbons being admixed with an aqueous solution of caustic alkali having a Baum gravity .of at least 30. The heated hydrocarbons and aqueous solution of caustic alkali is maintained at a temperature in the range between 300 and 350 F. in intimate contact for a time no less than about minutes to cause hydrolysis of acidic materials not removed in the neutralization step after the aforesaid acid treatment. Following the contacting operation, the admixture is separated into a hydrocarbon phase, a caustic alkali aromatic sulionate phase and a caustic alkali phase. The three phases are separately withdrawn and the hydrocarbon phase is heated to a. distillation temperature sufiicient to recover the desired aromatic hydrocarbons.

In the aforesaid Schutze and Browder et al. patents, it was necessary to heat the aromatic hydrocarbonat a temperature no greater than 525 F. because if a temperature in excess of that temperature was maintained in the distillation tower the caustic alkali aromatic sulfonate formed during the hydrolysis operation, which was carried over in part by the aromatic hydrocarbons, decomposed to form S02 and SO: under the distillation conditions.

My invention is based on the discovery that the aforesaid processes of Schutze and Browder et a1. may be improved to a remarkable extent by increasing the strength of the caustic alkali and 350 1 2, it has been found that the caustic alkali aromatic sulfonate is salted out during the hydrolysis and settling operation to form an intermediate phase between the aromatic hydrocarbon and the caustic alkali solution phases. Such phases may be accumulated and separately withdrawn from the hydrolysis and settling zone. By virtue of the salting out effect of the higher strength caustic alkali solution it is possible to distill at elevated temperatures without danger of decomposing alkali aromatic sulfonates into the aforementioned acidic gases. Furthermore, it has been possible, as a result of eliminating the caustic alkali aromatic sulfonate carry-over to operate the heating means of the distillation facilities for greatly increased lengths of time between cleanings compared with that of the aforesaid Schutze and Browder et al. teachings.

The feed stock to the process of the present invention may include the feed stocks disclosed by the aforesaid patentees, Schutze and Browder et al. and may generally be described as including an acid treated and caustic washed aromatic hydrocarbon feed including toluenes, xylenes, as well as the aromatic hydrocarbons having 9 or more carbon atoms in the molecule. The feed stock of the present invention is an acid treated, particularly a sulfuric acid treated, and caustic alkali washed aromatic hydrocarbon fraction, the purpose of the acid treatment being to remove an amount, usually 1% and more, of oleflns resulting from the conversion operation in the production of aromatic concentrates, such as by hydroforming operations. Such hydroiorming operations are well known and since they do not form a part of my invention will not be described in detail here. The purpose of the caustic washing operation in the preparation of the feed stock is to neutralize the acidic components in the hydrocarbon fraction resulting from the sulfuric acid treatment. However, neither the acid treatment nor the caustic washing operation results in a satisfactory product because of the formasolution to at least 30 Baum. ,When a caustic tion of acid components which resist the caustic washing operation. Therefore, in accordance with the patntees, Schutze and Browder et al., it was necessary to subject the treated fraction to a hydrolysis operation. My invention is an improvement in the hydrolysis operation and the description thereof will be directed to this particular operation.

The present invention will be further illustrated by reference to the drawing in which the single figure is a flow diagram of a, preferred mode of practice of the present invention.

aseacas Referring now to the drawing, numeral ii designates a charge tank in which has been accumulated a stock of acid-treated and caustic washed aromatic hydrocarbons as has been described in the aforesaid Schutze and Browder et al. patents. For purposes of description, it may be assumed that this acid treated and caustic washed feed stock is an aromatic concentrate containing approximately 80% or more of aromatics. This feed stock is withdrawn from tank it by line l2 containing pump it and preheater i l. Preheater it may be a steam heat exchanger or other heating means and the temperature of the feed stock is raised to a temperature in the range between 300 and 350 F. The feed stock prior to the heating operation is admixed with a small amount of water introduced by line i5 controlled by valve to. The purpose of admixing water with the feed stock at this point is to prevent excessive concentration of the aqueous caustic alkali solution with which the feed stock is subsequently contacted as will be described hereinafter. The hydrocarbon feed stock, having appreciable capacity for dissolving water from the aqueous solution at the temperatures employed, concentrates the solution unless water is added to it in amounts approximately equivalent to that dissolved. The amount of water injected at this point will usually be in the range from 0.5 to 1.5% by volume based on the feed stock. For example, for a, charge rate of 5,000 to 7500 bbls. of iced per day approximately 50 bbls. per day of water may be injected at the equivalent of line i 5. The admixture of water and feed stock in line I2 is heated to a temperature between 300 and 350 F. and discharged thereby into a hydrolyzer I! which includes a contacting and a settling section. In hydrolyzer I! the heated hydrocarbon is admixed with a caustic alkali solution, such sodium hydroxide, having a Baum gravity of at least 30 which is introduced thereto by line H! through sprays l9 from a source which will be described in more detail hereinafter. In the contacting section, generally indicated as 20 of hydrolyzer II, the hydrocarbon feed and the caustic alkali solution are intimately admixed for at least 10 minutes to cause a reaction between the acidic components and the caustic alkali solution introduced thereto. As will be noted from the drawing, hydrolyzer I1 is shown to be composed of a contacting section and a settling section generally indicated as 2|. In the settling section 2| the admixture of hydrocarbon feed and the caustic alkali separate into three phases, a hydrocarbon phase 22, a sodium aromatic sulfonate phase 23, indicated by the shaded portion, and a caustic alkali phase 24 which is shown as the lowermost phase in hydrolyzer I1. While the three phases are shown diagrammatically as extending across the hydrolyzer II, it is not clearly established whether or not the three phases exist as such in the contacting section generally indicated .as 20 but it has been established that the three phases do exist in the settling section generally indicated as 2|. Regardless of the existence of the three phases in contacting section 20 of hydrolyzer I1, there is withdrawn from the settling section 2| thereof a hydrocarbon phase which is withdrawn by line 25 for further treatment as will be described, a caustic alkali aromatic sulfonate phase which is withdrawn by line 26 from the intermediate layer 23 and a caustic alkali phase which is withdrawn by line 21 containing pump 28. A portion of this withdrawn caustic alkali may be discharged as used caustic by line 2'? controlled by valve 29 while a greater portion thereof is recycled through branch line 30 containing heater 3i wherein the temperature of the recycled caustic alkali solution is raised to a sufficient point to maintain in hydrolyzer H a temperature in the range between 300" and 350 F. This heated, recycled caustic is admixed with fresh caustic which is introduced from a source not shown by line i 8 controlled by valve 32 and the admixture of used and fresh caustic discharged by line it! through sprays l9 into the hydrocarbon introduced by line I2 into hydrolyzer IT.

The hydrocarbon phase withdrawn from settling section 2! and hydrolyzer ll discharges by line 25 into a distillation zone 33. Distillation zone 33 may include a series of fractional distillation towers but for simplicity of description is shown as a single tower. It is understood that distillation zone 33 will include internal battling equipment such as packing, Raschig rings, bell cap trays and other contacting means to insure intimate contact between vapor and liquids and to allow separation of the desired aromatic hydrocarbons. Conditions of temperature and pressure are adjusted in distillation zone 33 to with draw as overhead by line 34 any light fractions which may have been contained in the feed stock in tank I i. Distillation zone 33 is also provided with line 35 for withdrawal of the desired aromatic hydrocarbons. A bottoms fraction is withdrawn from distillation zone 33 by line 36 and is withdrawn in part from the system thereby and in part is discharged by branch line 31 into a heater 38 containing heating coils 39. Heater 38 is provided with the usual facilities'for heating hydrocarbons and which will include burners 41). The hydrocarbons pass by line 31 through coils 39 and then by line 4| back into distillation zone 33 to provide heat for the distillation operation.

Prior to the present invention difiiculty was encountered in heating coil 39 due to fouling of the coils by build up of a deposit of sodium aromatic sulfonates therein. Furthermore, the distillation operation was impaired by the fact that these sulfonates tended to decompose if a. t mperature in excess of 525 F. was realized. The build-up of the deposit inside the heater coils resulted in excessive firing or" the heater which, in turn, contributed to decomposition with formation of the deleterious acidic gases mentioned before. As a result it was necessary to shut down the distillation periodically to clean out the heater coil 39 and also it was necessary during the distillation operation to treat the overhead product for removal of acidic gases. In the practice of the present invention the problem has been substantially alleviated to the extent that it is unnecessary to clean the coils 39 except at infrequent intervals.

The present invention also contemplates that the hydrocarbon layer withdrawn by line 25 may be subjected to treatment with an aqueous medium to remove entrained alkaline salts which may be carried over from the settling section 2|. Provision is, therefore, made in line 25 by a valve 42 whereby the flow through line 25 to zone 33 may be routed by line 43 controlled by valve 44 into a settling "drum 45. The hydrocarbon phase passing through line 43 is admixed with hot water introduced by line 46 controlled by valve 41. The hot water is at a temperature in the range between 300 and 350 F. "and is introduced thereto from a source not shown. The hydrocarbon phase in line 43 and the hot water in line 46 is admixed in line 48 and the admixture is discharged thereby into settler 45 which is provided with a steam coil or other heating means, 49' for maintenance of the temperature therein in the range between 300 and 350 F. A hydrocarbon layer separates from the aqueous layer in drum 45, the hydrocarbon layer being withdrawn from the top thereof by line 50 controlled by valve and discharged back into line 25 for introduction into distillation zone 33 for separation as has been described. The aqueous layer is withdrawn by line 52 controlled by valve 53 and may be discharged to a sewer or may be recycled in part to line 46 by branch line 54 controlled by valve 55.

While the description taken with the drawing shows the use of hot water as the washing medium for the hydrocarbon phase in line 25, it is to be understood that other aqueous media may be used in lieu thereof. For example, hot water may be replaced with a dilute alkali solution having a Baum gravity no greater than 30. Usual- 1y, however, it will be desirable to use an alkaline solution having a Baum gravity lower than about 15. The hot water introduced by line 46 alternatively may be replaced by an alcoholic medium to remove any entrained alkaline salts in the hydrocarbon phase in line25. For example, a dilute solution of methyl alcohol may be emplayed.

The present invention will be further illustrated by reference to the following run in which a feed stock was charged to the hydrolyzer I! at a rate of 5000 to 7500 bbls. per day. This feed stock had previously been treated with sulfuric acid to remove olefins and had been neutralized with an aqueous solution of sodium hydroxide. The fraction had a boiling range between 200 and 475 F. and comprised toluene, xylenes and heavier aromatic materials as well as paraflinic hydrocarbons. The acid treatment to which the stock had been subjected included treatment with an amount of concentrated sulfuric acid equivalent to 18 to 22 bbls. of 100% H2804, per barrel of feed. This caustic neutralized fraction was admixed with approximately 50 barrels per day of water and then heated to a temperature in' the range of from 300 to 350 F. and contacted in hydrolyzer I! with sodium hydroxide solution having a Baum gravity in the range between 35 and 38. As a result of this operation, a, hydrocarbon layer was separated from the outlet from settling section 2| and subsequently distilled to recover the toluene and xylenes and to separate higher boiling materials. It was found that in hydrolyzer I! an intermediate layer of sodium aromatic sulfonates formed which was withdrawn periodically. The hydrocarbon layer was distilled without appreciable fouling of heater coil 39 and without appreciable, if any, formation of acidic gases. In accordance with the present invention it was possible to operate without coming down for a cleaning of heater coil 39 for a period of from 28 to 36 days between cleaning operations, whereas, prior to the practice of the present invention, when employing the processes as described in the aforesaid Schutze and Browder et a1. patents it was necessary to shut the unit down for cleaning the heater coil after operation periods of from '7 to 10 days. Furthermore, during the foregoing operations, prior to my invention, there was the presence of acidic gases to be coped with in the operation of distilla-.

tion zone 33. V

The nature and objects of the present inven- 6 tion having been fully described and illustrated, what I desire to claim as new and useful and to secure by Letters Patent is: r

1. In a method for treating a hydrocarbon fraction comprising aromatics and olefins in which the hydrocarbon fraction is contacted with acid to remove olefins, the resulting acid sludge separated, the acid contacted aromatic hydrocarbon fraction neutralized with a concentrated aqueous solution of caustic alkali and the caustic alkali separated therefrom, the steps of heating the contacted aromatic hydrocarbons to a temperat e in e range between 300 and 350 F., admixing the heated aromatic hydrocarbons with an aqueous solution of caustic alkali having a Baum gravity at least 30 ata temperature in the range between 300 and 350 F., maintaining said heated aromatic hydrocarbons in contact with said heated aqueous solution for a time no less than 10 minutes, separating said admixture into an aromatic hydrocarbon phase, a caustic alkali aromatic sulfonate phase, and a caustic alkali phase, separately withdrawing said aromatic hydrocarbon phase and heating it to a distillation temperature sufiicient to separate a desired aromatic hydrocarbon fraction, and recovering said fraction.

2. In a method 1" or treating a hydrocarbon fraction comprising aromatics and olefins in which thehydrocarbon fraction is contacted with acid to remove olefins, the resulting acid sludge separated, the acid contacted aromatic hydrocarbon fraction neutralized with a concentrated aqueous solution of caustic alkali and the caustic separated therefrom, the steps of heating the contacted aromatic hydrocarbons to a temperature in the range between 300 and 350 F., ad'- mixing the heated aromatic hydrocarbons with an aqueous solution of caustic alkali having a Baum gravity at least 30 at a temperature in the range between 300 and 350 F., maintaining said heated aromatic hydrocarbons in contact with said heated aqueous solution for a time no less than 10 minutes, separating said admixture into an aromatic hydrocarbon phase, a caustic alkali aromatic sulfonate phase, and a caustic alkali phase, separately withdrawing said phases, and heating said aromatic hydrocarbon phase to a distillation temperature sufficient to separate a desired aromatic hydrocarbon fraction, and recovering said fraction.

3. In a method for treating a hydrocarbon fraction comprising aromatics and olefins in which the hydrocarbon fraction is contacted with acid to remove olefins, the resulting acid sludge separated, the acid contacted aromatic hydrocarbon fraction neutralized with a concentrated aqueous solution of caustic alkali and the caustic alkali separated therefrom, the steps of heating the aromatic hydrocarbon fraction to a temperature in the range between 300 and 350 F., admixing the heated aromatic hydrocarbons with an aqueous solution of caustic alkali having a Baum gravity at least 30 at a temperature in the range between 300 and 350 F., maintaining said heated aromatic hydrocarbons in contact with said heated aqueous solution for a time no less than 10 minutes, separating said admixture into an aromatic hydrocarbon phase, a caustic alkali aromatic sulfonate phase, and a caustic alkali phase, separately withdrawing said phases, admixing-said aromatic hydrocarbon phase with an aqueous medium at a temperature in the-range between 300 and 350 F., separating said last admixture into an aromatic hydrocarbon layer aeeaaae and an aqueous layer, separately withdrawing said layers and heating said aromatic hydrocar= bon layer to a distillation temperature sufiicient to separate a desired aromatic hydrocarbon fraction, and recovering said fraction.

4. In a method for treating an aromatic hydrocarbon fraction comprising a major portion of aromatics having from 7 to 9 carbon atoms in the molecule and a minor portion of olefins wherein the aromatic hydrocarbons comprises approximately 80% by volume of said aromatic hydrocarbon fraction in which the aromatic hydrocarbon fraction is contacted with sulfuric acid to vremove olefins, the resulting acid sludge separated, the acid contacted aromatic hydrocarbon neutralized with a concentrated aqueous solution of caustic alkali and the caustic alkali separated therefrom, the steps of heating the contacted aromatic hydrocarbon fraction to a temperature of approximately 325 F., admixing the heated aromatic hydrocarbon with an aqueous solution of caustic alkali having a Baum gravity in the range between 35 and 38 Baum at a temperature of approximately 325 F., maintaining said heated aromatic hydrocarbon in contact with said heated aqueous solution for a time no less than 10 minutes, separating said admixture into an aromatic hydrocarbon phase, a caustic alkali aromatic sulfonate phase and a caustic alkali phase, withdrawing said caustic alkali aromatic sulfonate phase and discarding same, withdrawing said caustic alkali phase and admixing it with a sufficient amount of caustic alkali solution having a Baum gravity suflicient to maintain said aqueous solution of caustic alkali at a Baum gravity in the range between and 38, separately withdrawing said aromatic hydrocarbon phase and heating said aromatic hydrocarbon phase to a distillation temperature suflicient to separate therefrom aromatic hydrocarbons having from 7 to 9 carbon atoms in the molecule and recovering said aromatic hydrocarbons.

5. A method in accordance with claim 4 in which the contacted aromatic hydrocarbon is admixed 'with water prior to heating same and ad- .mixture thereof with the caustic alkali solution.

6. In a method for treating an aromatic hydrocarbon fraction comprising a major portion of aromatics having from 7 to 9 carbon atoms in the molecule and a minor portion of olefins wherein the aromatic hydrocarbons comprises approximately 80% by volume of said aromatic hydrocarbon fraction in which the aromatic hydrocarbon fraction is contacted with sulfuric acid to remove olefins, the resulting acid sludge separated, the acid contacted aromatic hydrocarbon neutralized with a concentrated aqueous solution of caustic alkali and the caustic alkali separated therefrom, the steps of admixing the contacted hydrocarbon fraction with water in an amount in the range between 0.5 and 1.5% based on the aromatic hydrocarbon fraction, heating the contacted aromatic hydrocarbon fraction and water to a temperature of approximately 325 F., admixing the heated aromatic hydrocarbon with an aqueous solution of caustic alkali having a Baum gravity in the range between 35 and 38 Baum at a, temperature of approximately 325 F., maintaining said heated aromatic hydrocarbon in contact with said heated aqueous solution for a time no less than 10 minutes, separating said admixture into an aromatic hydrocarbon phase, a caustic alkali aromatic sulfonate phase and a caustic alkali phase, withdrawing said caustic alkali aromatic sulfonate phase and discarding same, withdrawing said caustic alkali phase and admixing it with a suflicient amount of caustic alkali solution having a Baum gravity sufiicient to maintain said aqueous solution of caustic alkali at a Baum gravity in the range between 35 and 38, separately withdrawing said aromatic hydrocarbon phase, washing said aromatic hydrocarbon phase with an aqueous medium to remove entrained alkaline salts therefrom, separating said Washed aromatic hydrocarbon phase from said aqueous medium, and heating said washed aromatic hydrocarbon phase to a distillation temperature suificient to separate therefrom aromatic hydrocarbons having from 7 to 9 carbon atoms in the molecule and recovering said aromatic hydrocarbons.

7. A method in accordance with claim 6 in which the aromatic hydrocarbon phase is washed with water at a temperature in the range between 300 and 350 F.

PRENTISS S. VILES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,400,373 Schutze May 14, 1946 2,481,816 Browder et al Sept. 13,1949 

1. IN A METHOD FOR TREATING A HYDROCARBON FRACTION COMPRISING AROMATICS AND OLEFINS IN WHICH THE HYDROCARBON FRACTION IS CONTACTED WITH ACID TO REMOVE OLEFINS, THE RESULTING ACID SLUDGE SEPARATED, THE ACID CONTACTED AROMATIC HYDROCARBON FRACTION NEUTRALIZED WITH A CONCENTRATED AQUEOUS SOLUTION OF CAUSTIC ALKALI AND THE CAUSTIC ALKALI SEPARATED THEREFROM, THE STEPS OF HEATING THE CONTACTED AROMATIC HYDROCARBONS TO A TEMPERATURE IN THE RANGE BETWEEN 300* AND 350* F., ADMIXING THE HEATED AROMATIC HYDROCARBONS WITH AN AQUEOUS SOLUTION OF CAUSTIC ALKALI HAVING A BAUME GRAVITY AT LEAST 30* AT A TEMPERATURE IN THE RANGE BETWEEN 300* AND 350* F., MAINTAINING SAID HEATED AROMATIC HYDROCARBONS IN CONTACT WITH SAID HEATED AQUEOUS SOLUTION FOR A TIME NO LESS THAN 10 MINUTES, SEPARATING SAID ADMIXTURE INTO AN AROMATIC HYDROCARBON PHASE, A CAUSTIC ALKALI AROMATIC SULFONATE PHASE, AND A CAUSTIC ALKALI PHASE, SEPARATELY WITHDRAWING SAID AROMATIC HYDROCARBON PHASE AND HEATING IT TO A DISTILLATION TEMPERATURE SUFFICIENT TO SEPARATE A DESIRED AROMATIC HYDROCARBON FRACTION, AND RECOVERING SAID FRACTION. 